Conspicuously absent from the long list of animals that have inspired pop culture superheroes are shrews—small, mole-like mammals that love to eat insects. But perhaps these demure little creatures have shirked the spotlight for far too long.
Take, for instance, the hero shrew (technically, two species: Scutisorex somereni and Scutisorex thori)—an animal with an extraordinarily strong, flexible backbone that’s absurdly difficult to break. Stories of its remarkable resilience abound among the Mangbetu people of the Democratic Republic of the Congo, who reportedly astonished Western explorers in the 1910s by demonstrating that a grown man could stand on the tiny mammal’s back without hurting it.
This tale of anatomical heroism “may or may not be apocryphal,” says Stephanie Smith, a vertebrate functional morphologist at the Field Museum of Natural History in Chicago, in an interview with Jake Buehler at Science News.
But Smith and her colleagues now have solid data to back up other aspects of these creatures’ superpowered spines at a level of detail that’s never been seen before. By scanning the internal structures of the shrews’ vertebrae, they’ve come up with some theories about how their unusual anatomy evolved, and how the animals put it to use in daily life. The findings are reported this week in Proceedings of the Royal Society B.
As Jason Bittel reports for National Geographic, hero shrews—native to the Congo Basin—are tough to study in their natural habitat, much of which intersects with regions that have been troubled with political unrest in recent decades. Smith and paleontologist Kenneth Angielczyk turned instead to 16 hero shrew specimens already in the Field Museum’s collections. The pair scanned the animals’ skeletons, comparing them to those of four goliath shrews, which belong to a related species of similar size, but with a notably different spine.
Goliath shrews have vertebrae that, by and large, resemble the bones of other mammals, including us humans: Stacked atop one another in a somewhat loose formation, they’re sturdy but relatively thin, with a spongy interior. Hero shrews, Smith and Angielczyk found, have taken this motif and built enormously upon it, broadening and thickening the typical mammalian spine. Each of their vertebrae are dense and heavily reinforced—features that make the spine sturdier—and fringed with fingerlike projections that interlock the bones together when the shrews contract their muscles.
“It makes the unit more like a single block of bone than regular vertebrae, which are more like bendy units,” Smith tells Science News. This allows the shrews to scrunch their spines up like inchworms, according to a statement, and withstand an enormous amount of force for their weight and size, which is comparable to that of a rat.
The researchers still aren’t sure why hero shrews—and so far, it seems, only hero shrews—evolved these gnarly backbones. One theory posits that the little mammals’ super-strong help them wedge themselves into tight spaces at the base of palm trunks, where they forage for insects or larvae, though this has never been documented, Smith tells National Geographic.
“Backbones are an important part of how animals move, yet we understand surprisingly little about them,” Katrina Jones, an evolutionary biologist at Harvard University, tells Science News. Given how difficult it is to monitor hero shrews in the wild, the new study represents “an important step in understanding this adaptation.”